This invention relates to a process for removing polar bodies and contaminants, including color bodies, from unsaturated hydrocarbon streams having a boiling range between 280.degree.-310.degree. F. derived from the cracking of petroleum and coal (such streams hereinafter are called "unsaturated hydrocarbon streams"). Unsaturated hydrocarbon streams contain a number of contaminants and polar bodies which affect their color and purity, including color bodies, unwanted preformed polymers, sulfur containing compounds, compounds containing oxygen (hereinafter called oxygenates), including but not limited to aldehydes, ketones, peroxides, tetrahydrofurans, furans, ethers, including glycol ethers, hydroxy compounds, including phenols, glycols, catechols, resorcinol, hydroquinones, and other oxygenates, including but not limited to alcohols, glycols, phenolics, and hydroxybenzenes.
An important component of unsaturated hydrocarbon streams in the 280.degree.-310.degree. F. boiling range is styrene. Styrene is used in a wide variety of applications. For example, styrene is used to manufacture polystyrene products, such as cups, plates, packaging materials, and insulation. Important characteristics sought in a commercial styrene product are purity and lack of color. Thus, companies that produce styrene are under pressure to rid their styrene products of contaminants that increase the color or reduce the purity of the styrene. Styrene producers also are under pressure to rid their styrene products of contamination by sulfur, which can cause an unpleasant odor or undesirable color, and which can poison and/or consume catalysts used in subsequent reactions to which the styrene may be subjected.
Styrene is one product resulting from the refinement of petroleum crude oil. For example, styrene is a byproduct in the thermal pyrolysis of hydrocarbon streams, particularly naphthas and distillates derived from crude oil, to produce ethylene and propylene. The styrene is recovered as part of a pyrolysis gasoline product, consisting of organic molecules having five to nine carbon atoms, and having a boiling range of 280.degree.-310.degree. F. This styrene-rich gasoline stream can be treated according to the present invention. Styrene also is produced at other points in the petroleum refining process. See U.S. Pat. Nos. 3,684,665; 4,031,153; and 3,763,015; also Sato, M. Extract Styrene from Pyrolysis Gasoline. Hydrocarbon Processing (May 1973) 141-144. In addition, styrene can be obtained from the pyrolytic treatment of coal, for example, through destructive distillation. Additionally, the styrene referred to herein can be styrene intentionally produced such as by a manufacturing process from benzene and ethylene feedstocks or similar feedstocks. Further styrene produced by the dehyrogenation of ethyl benzene or dehydration of .alpha.-methyl benzyl alcohol (.alpha.-MBA) can be used herein.
Various methods of purifying such unsaturated hydrocarbon streams have been tried in the past; however, there is a need for an inexpensive, commercially feasible method for purifying such streams.